1. Field of the Invention
The present invention relates to an occupant restraint system, which protects an occupant in an automobile when the automobile is in a lateral collision.
2. Description of Related Art
An automobile is equipped with an occupant restraint system, which protects an occupant in the automobile when the automobile is in a collision. For example, an airbag is provided in an automobile as the occupant restraint system. The airbag is inflated so as to protect an occupant in the automobile. Further, the occupant restraint system is required not only for a collision in a back-and-forth direction but also for a lateral, i.e., side-to-side, impact. U.S. Pat. No. 7,076,353 (corresponding to JP-A-2004-262410) discloses an occupant restraint system, for example. A curtain airbag protects an occupant from crashing into a sidewall of an automobile interior, and a pretensioner restrains an occupant from being displaced by a lateral impact.
When an automobile receives a lateral impact, the automobile may roll over. The rollover of the automobile has a variety of patterns, and one of the patterns is a trip-over. In the trip-over, after an automobile sideslips, i.e., lateral displacement, the automobile trips over a step, e.g., curbstone, such that the automobile rolls over by an inertial force. Another pattern is a flip-over. In the flip-over, a wheel of an automobile runs on a curbstone, and the automobile rolls over by the impact.
In a conventional occupant restraint system, a rollover of an automobile is determined using signals detected by an acceleration sensor and an angular rate sensor. An airbag is inflated, when the automobile is determined to roll over. Even if the automobile does not roll over as a result by an external factor after the automobile is determined to roll over by the signals, an occupant restraint device, e.g., airbag, is activated. However, the activation of the airbag on a non-grounded side, that is, lateral impact receiving side, is especially not necessary.